If you or someone you know has cancer, you may find yourself researching alternative and natural therapies to potentially improve treatment outcomes and enhance overall health and quality of life.

Unfortunately, many natural products marketed for their anticancer or immune-boosting properties do not have research to support their effectiveness and can even be dangerous under certain circumstances.

Mistletoe is an alternative cancer therapy used in certain parts of the world.

This article explains what mistletoe is and whether it’s effective for improving quality of life, treatment outcomes, and symptoms in people with cancer.

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European mistletoe (Viscum album L.) is a medicinal plant that has been used as a treatment for cancer for more than a century (1).

It’s an evergreen semiparasitic plant that grows on certain trees and draws out water and nutrients. It’s native to Europe and Asia (2).

Extracts from mistletoe are used to treat a variety of conditions, including cancer.

Austrian philosopher Rudolph Steiner first recommended mistletoe extract as a potential cancer treatment in 1920, but Dutch physician Ita Wegman was the first to use it in a person with cancer (3).

Oral preparations of mistletoe are available as dietary supplements.

However, most research investigating the effects of mistletoe on cancer outcomes focuses on injection or intravenous delivery, both of which are prescribed in certain European countries (4).

Mistletoe extract is typically injected under the skin 2–3 times a week. The treatment may continue for weeks or even years (2).

Even though mistletoe is used as an alternative cancer therapy in European countries, mistletoe extract is not approved for use in the United States by the Food and Drug Administration (FDA).

Therefore, prescription mistletoe products are not available in the United States (4).

In Europe, mistletoe extracts are among the most prescribed therapies used to treat cancer. Mistletoe is most commonly prescribed in German-speaking countries.

Mistletoe products differ depending on the type of tree on which the mistletoe grows, the species of mistletoe, and the time of year it is harvested. Mistletoe extracts are made in water-based solutions or with a mixture of water and alcohol (5).

Mistletoe extracts are commonly used as an adjuvant treatment in people with cancer, meaning they are used after initial traditional cancer treatments such as chemotherapy.

Commercially available formulations of European mistletoe extracts include Helixor, Iscador, Iscador Qu, Lektinol, Cefalektin, Eurixor, ABNOBAviscum, and Abnoba-viscum Quercus (4, 5).

Summary

Mistletoe extracts are commonly prescribed to people with cancer in some European countries. Prescription mistletoe products are usually injected under the skin and are typically used in combination with traditional cancer treatments such as chemotherapy.

Mistletoe contains several compounds that may have therapeutic potential, including lectins, viscotoxins, flavonoids, oligo- and polysaccharides, membrane lipids, alkaloids, and more (2).

Although experts don’t yet fully understand how mistletoe’s potential anticancer properties work, it’s thought that the lectins concentrated in mistletoe may modulate the immune system, improving immune defenses and decreasing negative effects of cancer treatments (2).

Lectins are molecules that contain both carbohydrate and protein parts. These compounds can bind to and modulate cells (6).

Viscotoxins are another type of active compound found in mistletoe. They are believed to have anticancer effects (1).

However, research suggests that complete mistletoe extract has more powerful anticancer effects than the isolated compounds found in mistletoe, implying that all compounds found in mistletoe, not just lectins and viscotoxins, contribute to these effects (1).

Studies show that mistletoe affects the immune system in a variety of ways that may be beneficial in treating cancer and reducing side effects of cancer treatment.

For example, in human studies, mistletoe extract administration has been shown to increase numbers of natural killer cells (NK cells), which are immune cells that fight cancer (7, 8, 9).

Mistletoe has also been shown to have anti-inflammatory effects, and some research suggests it may act as an antiangiogenesis agent. This means it may prevent the spread of cancer by stopping the growth of new blood vessels, cutting off fuel supply to tumors (4, 5).

Summary

Mistletoe extract contains a variety of biologically active compounds that have powerful immune-modulating effects, which may be effective in cancer treatment.

Unlike many other complementary cancer treatments, mistletoe extract has been studied extensively in humans. In fact, more than 50 clinical trials have looked at the effects of mistletoe extract in people with cancer (5).

Some research suggests that mistletoe may be beneficial for improving quality of life, decreasing treatment-related side effects, increasing survival time, and improving symptoms in people with certain cancers.

However, not all studies have shown a benefit, and some researchers have questioned the quality of existing evidence.

A review of 26 studies found that quality of life, including pain and nausea, significantly improved in people with cancer who were prescribed mistletoe extract compared with people who received placebo treatments (2).

Yet the researchers noted a high risk of bias in the analyzed studies.

Conversely, a two-part review of 28 studies found that well designed studies showed little to no benefit of mistletoe treatment for quality of life or survival in people with various types of cancer, including colorectal, lung, and breast cancers (10, 11).

Another review investigated the effects of the prescription mistletoe extract product Iscador on the survival of people with cancer.

The review included 32 studies and concluded that, when used as an adjuvant treatment, Iscador led to better survival, especially in people with cervical cancer (12).

A 2013 randomized controlled trial also showed positive results related to Iscador.

The study included 220 people with advanced metastatic pancreatic cancer who were receiving only supportive care.

The results showed that the people treated with Iscador lived an average of 2 months longer than the placebo group and experienced fewer disease-related symptoms, including pain, nausea, diarrhea, anxiety, and fatigue (5, 12, 13) .

A study in 319 women with nonmetastasized breast cancer compared those who received only standard cancer treatment (chemotherapy) to those who underwent standard treatment combined with mistletoe extract.

At 12 months, the participants who received the combination mistletoe and standard treatment had an improvement in symptoms such as fatigue, insomnia, and physical functioning, while the standard treatment group experienced worsened symptoms (14).

A U.S. trial looking at Iscar, a mistletoe extract product, in combination with the chemotherapy drug Gemcitabine was completed in 2007, but the results have not yet been published (5, 15).

The unpublished trial looked at people with non-small cell lung cancer for whom one round of chemotherapy had not been effective (15).

While some of these results suggest that mistletoe may be beneficial in the treatment of certain cancers, researchers note that many of the completed studies have major weaknesses and that their findings may not be reliable.

More high quality studies are needed to fully understand how mistletoe extract affects people with cancer and whether it should be recommended as an alternative cancer therapy (5).

If you have cancer and are interested in learning more about mistletoe and its potential in treating cancer, consult your oncology team.

These medical experts know more about your diagnosis and treatment and can help you decide whether alternative and complementary treatments such as mistletoe can or should be used in your specific case.

Summary

Some research suggests that mistletoe extract may be beneficial in improving quality of life, survival, and symptoms in people with cancer. However, researchers have voiced concerns about the reliability and mixed results of existing studies.

In general, side effects related to mistletoe extracts reported in clinical studies have been minimal and non-life-threatening (5).

The most common side effects reported by people using mistletoe are:

  • headache
  • fever
  • chills
  • inflammation and soreness at injection sites
  • elevated white cell count

However, there have been some reports of severe allergic reactions to mistletoe, including a few reports of anaphylactic shock (5).

A small 2019 study found that treatment with mistletoe extract products, including Iscador and Helixor, was safe and not related to adverse effects in people with cancer who had preexisting autoimmune diseases, including Hashimoto’s thyroiditis and ulcerative colitis (16).

However, taking mistletoe dietary supplements, including teas, in large quantities can lead to dangerous side effects and can even be fatal (4).

These products are different from commercially available formulations such as Iscador, which are prescribed by doctors (4).

Additionally, although mistletoe extract is not associated with many adverse side effects when used in clinical settings, mistletoe plants and berries are poisonous to humans and should be avoided (5).

As mentioned above, although mistletoe extract is commonly used in cancer treatment in certain areas of Europe, prescription injectable mistletoe products like Iscador are not approved by the FDA and are not available in the United States.

Mistletoe has the potential to interact with certain medications and may lead to other, less common side effects, including low blood pressure and slow heart rate.

It’s critical to consult your oncology team before taking any mistletoe products.

Your oncology team can help you decide the best course of treatment for your specific needs and can give you advice on appropriate evidence-based complementary treatments.

Summary

Study results suggest that prescription mistletoe products are generally safe. However, if you have cancer, discuss any medication or supplement changes with your oncology team to ensure safety.

Mistletoe extract is among the most widely studied complementary and alternative cancer therapies and is commonly prescribed to people with cancer in some European countries.

However, prescription mistletoe products are not approved for treating cancer in the United States.

Some research suggests that, when used as an adjuvant therapy, mistletoe extract may be effective for improving quality of life, symptoms, and survival in people with certain types of cancer.

However, not all studies have shown positive results, and some researchers have questioned the reliability of existing findings.

If you’re interested in mistletoe, or any other alternative cancer therapy for that matter, it’s critical that you consult your oncology team before taking any pharmaceutical or dietary supplement marketed toward people with cancer.